Crushers, shredders, hammermills, and ringmills are devices used to process scrap (usually metal) materials and stone, to crush or reduce the size of the material so that it can be more easily handled by other equipment for further processing or use.
Crushers are machines that typically include a plurality of hammers or rings mounted about a horizontal rotatable or rotor shaft. As the shaft rotates, the hammers or rings engage and crush whatever material is introduced into the crusher. The hammers or rings can be mounted on the shaft between supports in the form of spiders or center discs arranged or stacked together with spacers to provide a consistent gap between the spiders or discs. At the ends of the discs or spiders is a pair of end discs at each end of the shaft. The shaft extends outside of the crusher machine and the shaft is supported by bearings and rotated by a motor. Typically, the rotor shaft is cylindrical. The use of a cylindrical shaft requires that the supports be positively keyed to the shaft, for example, by using a square or rectangular key on the support and a corresponding keyway on the shaft, so that the support cannot rotate relative to the shaft. The use of a keyway weakens the main shaft and makes removal of the supports and the end discs a much more difficult task. Further, the key will weaken over time and eventually the rotor assembly will shift between the shredder housings. Obviously, this can necessitate a repair of the crusher/shredder, requiring that operation of the crusher/shredder be stopped for the duration of the repair. Depending on the location of the support which is no longer positively fixed with respect to the shaft, the crusher/shredder can be shut down for a considerable period of time.
Typically, the discs and spiders on larger crusher machines are manufactured or assembled with an interference fit where the bores of the discs and spiders are smaller than the diameter of the shaft. Only by heating the discs and the spiders will the bores open up due to thermal expansion and allow for installation on the rotor shaft. Normally the rotor stack is held together with a number of drawbars or tie rods to span the width of the rotor and they are threaded on each end. A drawbar is a solid cylindrical rod structure. One drawbar is placed into each hole, with a typical rotor assembly using four to six bars. A large nut is threaded onto each end of the drawbars and tightened to a high torque value by using a hydraulic wrench. Once the nuts are torqued to a specific value, a fabricated lock plate that has a hex bore and a round contour for the outside profile is placed in the counter bore in the end disc and fit around the nut. This lock plate is then welded to the end plate to prevent the nut from turning.
As the crusher machine is operated, the rotor assembly takes multiple hits and is subjected to substantial shock loads. The bores of the discs or spiders can be damaged by these shock loads over time. Damage to the bores will loosen up the interference fit and cause the discs or spiders to move on the shaft. Any axial movement is resisted by the preload provided by the rotor drawbars. However, if the movement becomes too great, the drawbars can be stressed past their yield point and suffer plastic deformation. Any rotation or movement of a particular disc or spider can also place the drawbar into a shear loading situation, which can break the drawbar. Once the drawbars have failed or broken, the drawbars are useless and no longer protect the crusher. At this point, the crusher will have to be repaired or if the damage is too great then the crusher may have to be discarded.
The present disclosure is designed to obviate and overcome many of the disadvantages and shortcomings experienced with prior drawbars for holding a rotor stack together. Moreover, the present disclosure is related to a pretensioning cable assembly that can hold a rotor stack together or a pretensioning cable assembly that can be used to retrofit or repair existing crushers having drawbars.